Hydroboration of unsaturated fatty acid methyl esters and conversion of the boron adducts*

Abstract

Unsaturated fatty acid methyl esters (FAMEs) can be modified to higher value compounds by hydroboration of the double bond. The added boron atom can be replaced in a subsequent oxidation by a hydroxy group. This way methyl 10-undecenoate (1b), methyl oleate (3a), methyl ricinoleate ((9Z,12R)-6a), and methyl linoleate (9) were converted into methyl 11-hydroxyundecanoate and methyl hydroxyoctadecanoates in 82-92% yield. Organoboranes isomerize at higher temperatures. Hydroboration of oleic acid and subsequent heating to 220°C led after oxidative work-up to 70% of 1,4octadecanediol. Presumably a 1,4-oxaborinane intermediate is involved. Alkyl groups of organoboranes can be attached to the carbonyl-equivalent: dichloromethyl methyl ether (DCME). With this reaction the boranes of the esters 1b and 3a were converted in 55-80% yield to dimers with an inserted ketocarbonyl group. Ester 9 afforded in the same reaction methyl nonadecanoates with an integrated cyclopentene ring.Practical applications: Hydroboration-oxidation allows the partially regioselective conversion of unsaturated FAMEs into hydroxy-and dihydroxyesters. Thermal isomerization of the boranes from methyl oleate, oleic acid, and oleyl alcohol leads after oxidative work-up to the 1,4-diol: 1,4octadecanediol as main product. These products are useful as components for polyesters, polyurethanes, and precursors for heterocycles. Reaction of organoboranes from unsaturated FAMEs with the carbonyl equivalent: DCME provides a one-step access to 1,v-diesters with an internal keto group, which can be applied for coupling, cross-linking, and further conversion. The borane · THF complex is commercially available in amounts of 0.8 mol and more to do exploratory research toward such applications.

Synthesis of Functionalized High‐Oleic Soybean Oil Wax Coatings and Emulsions for Postharvest Treatment of Fresh Citrus Fruit

“…HOSO was functionalized with single hydroxyl moieties via hydroboration–oxidation following previous work on fatty acid methyl esters (FAMEs). [ 14 ] Addition of BTHF to HOSO results in the rapid formation of a clear, extremely viscous, and rigid gel at either low temperatures, sub stoichiometric BTHF, or dilution of HOSO with dry THF. Gelling during hydroborations has been reported for diverse olefinic substrates, [ 15–17 ] although this is not typical of FAMEs.…”

“…Previous reports propose the formation of cyclic five membered borolanes to explain the presence of two isomeric 1,4‐diols from the hydroboration–oxidation of methyl linoleate. [ 14 ] This behavior may be contributing to both the initial preference for the monoalkylborane and increase in viscosity since the geometry of TAG‐linoleate chains would be modified in such a way that undue strain would be added onto the system. Bulkier hydroborating agents (i.e., thexylborane, pinacolborane) were entirely avoided due to their steric implications and cost since BTHF is comparatively less expensive and readily available.…”

Isomerization‐hydroboration‐oxidation strategy: Access to long chain AB‐ and AA‐type oleyl based monomers and polymers thereof

“…Oxidation of hydroborated oleyl carbamate using 30% H 2 O 2 solution was performed according to a procedure already reported .…”

“…The resulting light yellow solution was diluted with 100 mL of methylene chloride and filtered through silica gel to remove the catalyst. The filtrate was then evaporated under reduced pressure and the obtained mixture on flash chromatographic separation gave a white solid-0.51 g (61% yield), which was analyzed by 1 H, 13 C, and 11 Oxidation of hydroborated oleyl carbamate using 30% H 2 O 2 solution was performed according to a procedure already reported [19,26].…”

“…al. demonstrated that hydroboration‐thermal isomerization followed by oxidation of boronated adduct could lead to different diols starting from oleyl alcohol. However, high temperature around 220°C is required for the thermal isomerization of boronated adducts.…”